A known electric pump is disclosed in JP2006-336469A (which is hereinbelow referred to as reference 1). According to the electric pump in reference 1, a trochoid-type pump portion is configured by providing an inner rotor in an outer rotor. A rotor is formed by providing a permanent magnet along an outer circumferential surface of the outer rotor. A casing is provided at a position surrounding the outer rotor. A stator, around which plural wires are respectively wound, is provided at a portion of the casing surrounding the outer rotor. Electric power is supplied to each of the wires of the stators by an inverter circuit, thereby the outer rotor is rotated, and the inner rotor is rotated accompanying the rotation of the outer rotor, so as to function as a pump.
For example, in an electric pump which supplies lubricating oil to an engine of a vehicle, a relief valve is provided at an oil passage, through which operation fluid is discharged from the electric pump, so as to prevent oil from being excessively pressurized.
In a case where a relief valve is provided at an oil passage system, assembly of an oil passage system may require time and labor. In order to simplify the tasks required for assembling the oil passage system, a relief valve may be provided between a suction port and a discharge port of the electric pump, as disclosed in JP60-149892.
In such a case where the relief valve is provided between the suction port and the discharge port, a thickness of a whole electric pump in a direction of a rotational axis is enlarged, thus to upsize the electric pump per se.
A need thus exits for an electric pump that is not susceptible to the drawback mentioned above.